The Fred Hutchinson Cancer Research Center (FHCRC) brings together more than 200 FHCRC faculty with research interests in basic, clinical and public health sciences. To remain competitive with peer institutions, the FHCRC must be capable of accommodating the Animal Health Resource (AHR) space needs for new faculty and growth in the existing programs. There are presently 79 investigators on the FHCRC South Lake Union utilizing animals in approximately 200 active and approved IACUC protocols for their programs of study within the existing facilities. The AHR department has experienced an approximate 69% increase in care days over the past 4 fiscal years, with most of the increase principally due to expanding use of genetically modified rodents among existing faculty. Addition of new faculty to the FHCRC and expanding needs of current investigators are expected to contribute to a continuation of this trend. The FHCRC is currently completing an initial transition to individually ventilated and HEPA filtered caging for its rodent colonies, which will allow increased housing density within existing facility space for its animal populations. Currently there is a need to meet the growing demand, with continued installation and expansion of ventilated rack capacity. Funding is requested for the purchase of 17 double faced and 19 single faced ventilated rack systems with associated accessories. The additional racks requested will allow us to maximize animal housing densities within the existing facility, providing benefit to all Center faculty who rely upon mouse models for their cancer related research projects. There are comprehensive and complementary animal facility use procedures in conjunction with the ventilated caging that address personnel and material flow in all areas of use to provide for exclusion of rodent pathogens which could jeopardize animal health and scientific quality.